通过 SMTP 发送电子邮件时出错

我正在尝试使用 gmail 作为 SMTP 通过 Java 代码发送电子邮件。但出现如下异常。请告诉我为什么找不到 gmail 主机。我在办公室网络中工作，不确定是否某些防火墙阻止其发送。如果是的话，出路是什么？

Exception in thread "main" com.sun.mail.util.MailConnectException: Couldn't connect to host, port: smtp.gmail.com, 586; timeout -1;
  nested exception is:
    java.net.UnknownHostException: smtp.gmail.com
    at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:2053)
    at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:697)
    at javax.mail.Service.connect(Service.java:364)
    at javax.mail.Service.connect(Service.java:245)
    at mail.JavaEmail.sendEmail(JavaEmail.java:72)
    at mail.JavaEmail.main(JavaEmail.java:22)
Caused by: java.net.UnknownHostException: smtp.gmail.com

Java源代码：

package mail;

import java.util.Properties;

import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.AddressException;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

public class JavaEmail
{
    Session mailSession;

    public static void main(String args[]) throws AddressException,    MessagingException
    {
        JavaEmail javaEmail = new JavaEmail();
        javaEmail.setMailServerProperties();
        javaEmail.draftEmailMessage();
        javaEmail.sendEmail();
    }

    private void setMailServerProperties()
    {
        Properties emailProperties = System.getProperties();
        emailProperties.put("mail.smtp.port", "586");
        emailProperties.put("mail.smtp.auth", "true");
        emailProperties.put("mail.smtp.starttls.enable", "true");
        mailSession = Session.getDefaultInstance(emailProperties, null);
    }

    private MimeMessage draftEmailMessage() throws AddressException, MessagingException
    {
        String[] toEmails = { "[email protected] /cdn-cgi/l/email-protection" };
        String emailSubject = "Test email subject";
        String emailBody = "This is an email sent by JAVA Code";
        MimeMessage emailMessage = new MimeMessage(mailSession);
        /**
         * Set the mail recipients
         * */
        for (int i = 0; i < toEmails.length; i++)
        {
            emailMessage.addRecipient(Message.RecipientType.TO, new InternetAddress(toEmails[i]));
        }
        emailMessage.setSubject(emailSubject);
        /**
         * If sending HTML mail
         * */
        emailMessage.setContent(emailBody, "text/html");
        /**
         * If sending only text mail
         * */
        //emailMessage.setText(emailBody);// for a text email
        return emailMessage;
    }

    private void sendEmail() throws AddressException, MessagingException
    {
        /**
         * Sender's credentials
         * */
    String fromUser = "[email protected] /cdn-cgi/l/email-protection";
        String fromUserEmailPassword = "*****";

        String emailHost = "smtp.gmail.com";
        Transport transport = mailSession.getTransport("smtp");
        transport.connect(emailHost, fromUser, fromUserEmailPassword);
        /**
         * Draft the message
         * */
        MimeMessage emailMessage = draftEmailMessage();
        /**
         * Send the mail
         * */
        transport.sendMessage(emailMessage, emailMessage.getAllRecipients());
        transport.close();
        System.out.println("Email sent successfully.");
    }
}

您连接到了错误的端口。 Google 的 TLS SMTP 服务器是587。您可以在此处查看更多相关信息：http://email.about.com/od/accessinggmail/f/Gmail_SMTP_Settings.htm http://email.about.com/od/accessinggmail/f/Gmail_SMTP_Settings.htm